President Obama on Tuesday promised several thousand military veterans that he would fulfill his "sacred trust" to those returning from America's wars by overhauling a dysfunctional health care system, even as a new report documented "unacceptable and troubling lapses" in medical treatment. Addressing the American Legion's national convention three months after a scandal rocked the Department of Veterans Affairs and forced the resignation of the agency's leader, Mr. Obama said he had "made real progress" in improving services and getting patients off waiting lists. But he added that he was "very clear eyed about the problems that still are there" and about the need to "regain the trust" of veterans.